CA1336126C - Process for the concentration of sulfuric acid by evaporation - Google Patents
Process for the concentration of sulfuric acid by evaporationInfo
- Publication number
- CA1336126C CA1336126C CA000568421A CA568421A CA1336126C CA 1336126 C CA1336126 C CA 1336126C CA 000568421 A CA000568421 A CA 000568421A CA 568421 A CA568421 A CA 568421A CA 1336126 C CA1336126 C CA 1336126C
- Authority
- CA
- Canada
- Prior art keywords
- evaporation
- sulfuric acid
- concentration
- iron
- concentrated
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/90—Separation; Purification
- C01B17/901—Recovery from spent acids containing metallic ions, e.g. hydrolysis acids, pickling acids
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/88—Concentration of sulfuric acid
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Electrolytic Production Of Metals (AREA)
Abstract
A process for the concentration by evaporation of 60 to 75 % sulfuric acid containing metal sulfates, comprising concentrating 60 to 75 % sulfuric acid containing metal sulfates to a concentration of 85 to 96 % H2SO4 by evaporation in vacuo at a temperature of 150 to 220°C, the sulfuric acid to be concentrated by evaporation containing less than 0,01 % by weight and preferably less than 0,005 % by weight iron(III) ions.
Description
A PROCESS FOR THE CONCE~ATION OF ~IF~C ACID BY
EVAPORATION
BACKGROUND OF THE INVENTION
Field of the invention This invention relates to a process for the con-centration by evaporation of 60 to 75 % sulfuric acid containing metal sulfates.
BACKGROUND INFORMATION
US 3,280,156 describes a process for working up sulfuric acid containing metal sulfates, so-called waste acid , by concentration in immersion-heater evaporators, separation of the solid metal sulfates from the 60 to 70 % sulfuric acid and further concentration of this sulfuric acid by evaporation in cast iron boilers with dephlegmators at 300 to 330C to an H2S04 content of 93.5 to 95 %. After separation of the metal sulfates, this highly concentrated sulfuric acid is used in the digestion of the titanium raw material. Apart from the very high specific plant costs, the disadvantages of this process are its high energy consuption and the high repair costs.
According to EP-A 133 505, waste acid is con-centrated by evaporation in vacuo in several steps to such an extent that a suspension of metal sulfates in 62 to 70 % sulfuric acid is formed. This acid is used in the digestion of the titanium raw material either directly or after further concentration by evaporation to an H2S04 content of 75 to 85 %. The disadvantage of this process is that oleium is required to obtain the necessary concentration for the digesten reaction by mixing with the recovered acid.
SUMMARY OF THE INVENTION
The object of the present invention is to provide aprocess whcih does not have the disadvantages of the above described processen, According to the invention, this object is achieved Le A 25 124-US
in that the waste acid is concentrated by evaporation to such an extent that a 60 to 75% sulfuric acid still containing dissolved metal sulfates is obtained after crystallization and separation of the solid metal sulfates. According to the invention, the sulfuric acid to be concentrated by evaporation must be substantially free from iron(III) ions.
This sulfuric acid is then concentrated by evaporation in vacuo at 150 to 220C to a concentration of 85 to 96% H2SO4 (based on salt-free acid). Accordingly, the present inven-tion also relates to a process for the concentration by evaporation of 60 to 75% sulfuric acid containing metal sulfates which is characterized in that the 60 to 75~ sul-furic acid containing metal sulfates is concentrated by evaporation in vacuo at temperatures of 150 to 220C to a concentration of 85 to 96~ H2SO4, the sulfuric acid to be concentrated by evaporation containing less than 0.01~ by weight and preferably less than 0.005% by weight iron(III) ions. The sulfuric acid obtained in this way may be used either on its own or together with concentrated salt-free sulfuric acid in the digestion of the raw material.
DETAILED DESCRIPTION OF THE INVENTION
In one preferred embodiment of the process according to the invention, the concentration of the sulfuric acid containing metal sulfates by evaporation is carried out in horizontal evaporators or forced-circulation evaporators with tantalum heat exchangers. It is of equal advantage to carry out the evaporation according to the invention in forced-circulation evaporators with enamelled heat transfer surfaces. One such evaporator system is described in EP-B 22 181.
There has been no shortage of attempts in the past to concentrate sulfuric acids containing metal sulfates to relatively high concentrations. In general, however, the heat exchanger surfaces generally became encrusted which impaired evaporation efficiency or meant that the process had to be interrupted for the heat exchangers to be cleaned.
Le A 2S 124 - 2 -1 3361 2-~
1 It has now surprisingly been found that these deposits of metal sulfates are not formed on the heat transfer surfaces in the process according to the invention. A low content of iron(III) ions in the sulfuric acid to be concentrated is partly responsible for this. The need for a low iron(III) content becomes essential in particular when the sulfuric acid containing metal sulfates is concentrated by evaporation to concentrations above 92% H2SO4. In this case, the iron(III) content of the 60 to 75% sulfuric acid should be below 50 ppm. To this end, reducing agents are added to the sulfuric acid to be concentrated by evaporation. In one particularly advantageous embodiment of the process according to the invention, this is done by addition of sodium formaldehyde sulfoxylate as a reducinq agent. However, it is also possible to establish the necessary 7OW iron (III) ion content by addition of metallic iron or by electro-chemical reduction.
Depending on the titanium raw material, the chromium and vanadium ion content of the 62 to 70% sulfuric acid recovered can have a troublesome effect on the pigment pro-duction process. After this acid has been concentrated by evaporation to a concentration of 75 to 85% H2SO4, the metal sulfates are precipitated in a finely divided form which is extremely difficult to filter, so that the quality of the acid can hardly be improved. However, it has surprisingly been found that, after the sulfuric acid recovered has been concentrated by evaporation in accordance with the invention to a concentration of 85 to 96% H2SO4, the metal sulfates crystallize in a more filterable form. Accordingly, a further object of the process according to the invention is to improve the quality of the sulfuric acid recovered by separation of the metal sulfates, particularly the heavy metal sulfates, which crystallize during cooling~O a temperature below 100C. The metal su1fates may be separated off in ~ncwn manner by filtration or centrifugation.
Le A 25 124 1 The chromium content of the 85-96% sulfuric acid separated off from the solid metal sulfates and hydrogen sulfates is distinctly lower than that of the 60 to 75%
sulfuric acid so that, even where the acid recovered makes up a large part of the acid required for digestion of the raw material, there is no danger of the quality of the pigment being influenced by the sulfuric acid recovered.
The following Examples are intended to illustrate the process according to the invention without limiting it in any way.
COMPARISON EXAMPLE:
Sulfuric acid recovered from wasteacid by concentration by evaporation and separation of the solid metal sulfates had the following composition (in % by weight): 64.2% H~SO4;
0.08% Fe ; 0.06% Fe3 , 0.3% Al , 0.4% Mg ; 0.02% Cr 0.004% V3+.
This acid was concentrated by evaporation to a concen-tration of 92.6% H2SO4 (based on salt-free sulfuric acid) in a horizontal evaporator (enamelled steel container with a tantalum multi-pass heat exchanger) at 40 mbar and at an acid exit temperature of 185C. Over a period of 1 week, the sulfuric acid concentration fell to 90.3% for otherwise unchanged operating conditions. After the evaporator had been emptied and cleaned, the concentration of 92.6% was re-established.
E~AMPLE 1 2 g sodium formaldehyde sulfoxylate per liter were added to sulfuric acid having the same composition as in the Comparison Example before it was introduced into the horizontal evaporator. The Fe3 content of the acid introduced was 0.004%. Over an operating period of 2 weeks, no reduction was observed in the evaporation efficiency.
Le A 25 124 -Preconcentrated sulfuric acid (recovered from waste acid) was further concentrated by evaporation at 220C/60 mbar absolute pressure in a forced-circulation evaporator of enamelled steel with enamelled double-walled tubes in which the heat of evaporation was supplied by a heat carrier oil.
The concentrated sulfuric acid flowing out from the evaporator was cooled to a temperature of 62C and filtered in a pressure filter. The quality of the sulfuric acid recovered in accordance with EP-A 133 505 and of the sulfuric acid further concentrated and filtered in accordance with the invention are compared in the following Table.
Composition of the sulfuric acid (~ by weight) Preconcentrated Concentrated acid acid H2SO4 65.3 94.7 FeSO4 0.11 0.04 Fe2(SO4)3 0.015 0.01 MgSO4 2.0 0.19 A12(SO4)3 1.5 0.14 4 0.03 0 005 4 0-037 0.002 VOSo4 0.003 0.002 Cr2(SO4)3 0 047 0.008 Le A 25 124 It will be appreciated that ~he instant speci-fication and claims are set forth by way of illustration and not limitation and that various modifications and changes may be made without departing from the spirit and scope of the present invention.
~0 ~5 Le A 25 124
EVAPORATION
BACKGROUND OF THE INVENTION
Field of the invention This invention relates to a process for the con-centration by evaporation of 60 to 75 % sulfuric acid containing metal sulfates.
BACKGROUND INFORMATION
US 3,280,156 describes a process for working up sulfuric acid containing metal sulfates, so-called waste acid , by concentration in immersion-heater evaporators, separation of the solid metal sulfates from the 60 to 70 % sulfuric acid and further concentration of this sulfuric acid by evaporation in cast iron boilers with dephlegmators at 300 to 330C to an H2S04 content of 93.5 to 95 %. After separation of the metal sulfates, this highly concentrated sulfuric acid is used in the digestion of the titanium raw material. Apart from the very high specific plant costs, the disadvantages of this process are its high energy consuption and the high repair costs.
According to EP-A 133 505, waste acid is con-centrated by evaporation in vacuo in several steps to such an extent that a suspension of metal sulfates in 62 to 70 % sulfuric acid is formed. This acid is used in the digestion of the titanium raw material either directly or after further concentration by evaporation to an H2S04 content of 75 to 85 %. The disadvantage of this process is that oleium is required to obtain the necessary concentration for the digesten reaction by mixing with the recovered acid.
SUMMARY OF THE INVENTION
The object of the present invention is to provide aprocess whcih does not have the disadvantages of the above described processen, According to the invention, this object is achieved Le A 25 124-US
in that the waste acid is concentrated by evaporation to such an extent that a 60 to 75% sulfuric acid still containing dissolved metal sulfates is obtained after crystallization and separation of the solid metal sulfates. According to the invention, the sulfuric acid to be concentrated by evaporation must be substantially free from iron(III) ions.
This sulfuric acid is then concentrated by evaporation in vacuo at 150 to 220C to a concentration of 85 to 96% H2SO4 (based on salt-free acid). Accordingly, the present inven-tion also relates to a process for the concentration by evaporation of 60 to 75% sulfuric acid containing metal sulfates which is characterized in that the 60 to 75~ sul-furic acid containing metal sulfates is concentrated by evaporation in vacuo at temperatures of 150 to 220C to a concentration of 85 to 96~ H2SO4, the sulfuric acid to be concentrated by evaporation containing less than 0.01~ by weight and preferably less than 0.005% by weight iron(III) ions. The sulfuric acid obtained in this way may be used either on its own or together with concentrated salt-free sulfuric acid in the digestion of the raw material.
DETAILED DESCRIPTION OF THE INVENTION
In one preferred embodiment of the process according to the invention, the concentration of the sulfuric acid containing metal sulfates by evaporation is carried out in horizontal evaporators or forced-circulation evaporators with tantalum heat exchangers. It is of equal advantage to carry out the evaporation according to the invention in forced-circulation evaporators with enamelled heat transfer surfaces. One such evaporator system is described in EP-B 22 181.
There has been no shortage of attempts in the past to concentrate sulfuric acids containing metal sulfates to relatively high concentrations. In general, however, the heat exchanger surfaces generally became encrusted which impaired evaporation efficiency or meant that the process had to be interrupted for the heat exchangers to be cleaned.
Le A 2S 124 - 2 -1 3361 2-~
1 It has now surprisingly been found that these deposits of metal sulfates are not formed on the heat transfer surfaces in the process according to the invention. A low content of iron(III) ions in the sulfuric acid to be concentrated is partly responsible for this. The need for a low iron(III) content becomes essential in particular when the sulfuric acid containing metal sulfates is concentrated by evaporation to concentrations above 92% H2SO4. In this case, the iron(III) content of the 60 to 75% sulfuric acid should be below 50 ppm. To this end, reducing agents are added to the sulfuric acid to be concentrated by evaporation. In one particularly advantageous embodiment of the process according to the invention, this is done by addition of sodium formaldehyde sulfoxylate as a reducinq agent. However, it is also possible to establish the necessary 7OW iron (III) ion content by addition of metallic iron or by electro-chemical reduction.
Depending on the titanium raw material, the chromium and vanadium ion content of the 62 to 70% sulfuric acid recovered can have a troublesome effect on the pigment pro-duction process. After this acid has been concentrated by evaporation to a concentration of 75 to 85% H2SO4, the metal sulfates are precipitated in a finely divided form which is extremely difficult to filter, so that the quality of the acid can hardly be improved. However, it has surprisingly been found that, after the sulfuric acid recovered has been concentrated by evaporation in accordance with the invention to a concentration of 85 to 96% H2SO4, the metal sulfates crystallize in a more filterable form. Accordingly, a further object of the process according to the invention is to improve the quality of the sulfuric acid recovered by separation of the metal sulfates, particularly the heavy metal sulfates, which crystallize during cooling~O a temperature below 100C. The metal su1fates may be separated off in ~ncwn manner by filtration or centrifugation.
Le A 25 124 1 The chromium content of the 85-96% sulfuric acid separated off from the solid metal sulfates and hydrogen sulfates is distinctly lower than that of the 60 to 75%
sulfuric acid so that, even where the acid recovered makes up a large part of the acid required for digestion of the raw material, there is no danger of the quality of the pigment being influenced by the sulfuric acid recovered.
The following Examples are intended to illustrate the process according to the invention without limiting it in any way.
COMPARISON EXAMPLE:
Sulfuric acid recovered from wasteacid by concentration by evaporation and separation of the solid metal sulfates had the following composition (in % by weight): 64.2% H~SO4;
0.08% Fe ; 0.06% Fe3 , 0.3% Al , 0.4% Mg ; 0.02% Cr 0.004% V3+.
This acid was concentrated by evaporation to a concen-tration of 92.6% H2SO4 (based on salt-free sulfuric acid) in a horizontal evaporator (enamelled steel container with a tantalum multi-pass heat exchanger) at 40 mbar and at an acid exit temperature of 185C. Over a period of 1 week, the sulfuric acid concentration fell to 90.3% for otherwise unchanged operating conditions. After the evaporator had been emptied and cleaned, the concentration of 92.6% was re-established.
E~AMPLE 1 2 g sodium formaldehyde sulfoxylate per liter were added to sulfuric acid having the same composition as in the Comparison Example before it was introduced into the horizontal evaporator. The Fe3 content of the acid introduced was 0.004%. Over an operating period of 2 weeks, no reduction was observed in the evaporation efficiency.
Le A 25 124 -Preconcentrated sulfuric acid (recovered from waste acid) was further concentrated by evaporation at 220C/60 mbar absolute pressure in a forced-circulation evaporator of enamelled steel with enamelled double-walled tubes in which the heat of evaporation was supplied by a heat carrier oil.
The concentrated sulfuric acid flowing out from the evaporator was cooled to a temperature of 62C and filtered in a pressure filter. The quality of the sulfuric acid recovered in accordance with EP-A 133 505 and of the sulfuric acid further concentrated and filtered in accordance with the invention are compared in the following Table.
Composition of the sulfuric acid (~ by weight) Preconcentrated Concentrated acid acid H2SO4 65.3 94.7 FeSO4 0.11 0.04 Fe2(SO4)3 0.015 0.01 MgSO4 2.0 0.19 A12(SO4)3 1.5 0.14 4 0.03 0 005 4 0-037 0.002 VOSo4 0.003 0.002 Cr2(SO4)3 0 047 0.008 Le A 25 124 It will be appreciated that ~he instant speci-fication and claims are set forth by way of illustration and not limitation and that various modifications and changes may be made without departing from the spirit and scope of the present invention.
~0 ~5 Le A 25 124
Claims (10)
1. A process for the concentration by evaporation of 60 to 75 % sulfuric acid containing metal sulfates, comprising concentrating the 60 to 75 % sulfuric acid containing metal sulfates to a concentration of 85 to 96 % H2SO4 by evaporation in vacuo at a temperature of 150 to 220°C, the sulfuric acid to be concentrated by evaporating having an iron(III) ion content of between 0 and 0,01 % by weight.
2. A process according to claim 1, wherein the weight % of iron(III) ions is between 0 and 0.005 %,
3. A process as claimed in claim 1, wherein the concentration by evaporation is carried out in a horizontal evaporator having a tantalum heat exchanger.
4. A process as claimed in claim 1, wherin the concentration by evaporation is carried out in a forced-circulation evaporator having a tantalum heat exchanger.
5. A process as claimed in claim 4, wherein the concentration by evporation is carried out in a forced-circulation evaporator having enammeled heat transfer surfaces.
6. A process as claimed in claim 1, wherein a reducing agent is added to the sulfuric acid to be concentrated by evaporation before the concentration by evaporation.
7. A process as claimed in claim 6 wherein the reducing agent is sodium formaldehyde sulfoxylate.
8. A process as claimed in claim 1, wherein the iron(III) ions are electrochemically reduced to iron(II) ions.
9. A process as claimed in claim 1, wherein the low iron(III) ion content is established by adding metallic iron.
10. A process as claimed in claim 1, wherein the quality of the concentrated acid is improved by separation of solid metal sulfates at temperatures below 100° C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3718675.2 | 1987-06-04 | ||
| DE19873718675 DE3718675A1 (en) | 1987-06-04 | 1987-06-04 | METHOD FOR EVAPORATING SULFURIC ACID |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1336126C true CA1336126C (en) | 1995-07-04 |
Family
ID=6329017
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000568421A Expired - Fee Related CA1336126C (en) | 1987-06-04 | 1988-06-02 | Process for the concentration of sulfuric acid by evaporation |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0293710B1 (en) |
| JP (1) | JP2659397B2 (en) |
| CA (1) | CA1336126C (en) |
| DE (2) | DE3718675A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102007059513A1 (en) * | 2007-12-11 | 2009-06-18 | Bayer Materialscience Ag | Process for the preparation of nitrobenzene by adiabatic nitration |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL273476A (en) * | 1961-01-26 | 1900-01-01 | ||
| EP0022181B1 (en) * | 1979-06-13 | 1983-10-12 | Bayer Ag | Process and apparatus for regenerating sulfuric acid |
| CH641126A5 (en) * | 1979-06-13 | 1984-02-15 | Bertrams Ag | Process and system for regenerating sulphuric acid |
| DE3327769A1 (en) * | 1983-08-02 | 1985-02-14 | Bayer Ag, 5090 Leverkusen | METHOD FOR THE TREATMENT OF THICK ACID |
| DE3329842A1 (en) * | 1983-08-18 | 1985-02-28 | Kronos Titan-Gesellschaft Mbh, 5090 Leverkusen | Process for substantially removing unwanted metal ions, in particular vanadium ions, when concentrating dilute iron(II) sulphate-containing sulphuric acid solutions |
-
1987
- 1987-06-04 DE DE19873718675 patent/DE3718675A1/en not_active Withdrawn
-
1988
- 1988-05-24 DE DE8888108227T patent/DE3865096D1/en not_active Expired - Lifetime
- 1988-05-24 EP EP88108227A patent/EP0293710B1/en not_active Expired - Lifetime
- 1988-05-30 JP JP63130478A patent/JP2659397B2/en not_active Expired - Fee Related
- 1988-06-02 CA CA000568421A patent/CA1336126C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0293710B1 (en) | 1991-09-25 |
| DE3718675A1 (en) | 1988-12-15 |
| EP0293710A2 (en) | 1988-12-07 |
| DE3865096D1 (en) | 1991-10-31 |
| JPS63310709A (en) | 1988-12-19 |
| EP0293710A3 (en) | 1989-07-26 |
| JP2659397B2 (en) | 1997-09-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |